[15.14] Chandra observations of NGC 253: New insights into the nature of starburst-driven superwinds

Arcsecond-resolution X-ray imaging of the nucleus of the
nearby starburst galaxy NGC 253 with Chandra reveals a
well-collimated, strongly limb-brightened, kiloparsec-scale
conical outflow from the central starburst region. The
outflow is very similar in morphology to the known
H{\alpha}~outflow cone, on scales down to \lesssim 20
pc.

This provides, for the first time, robust evidence that both
X-ray and H{\alpha}~emission come from low volume filling
factor regions of interaction between the fast energetic
wind of SN-ejecta and the denser ambient interstellar medium
(ISM), and not from the wind fluid itself. We provide
estimates of the (observationally and theoretically
important) filling factor of the X-ray emitting gas, of
between ~4 and 40 per cent, consistent with an upper
limit of ~40 per cent based directly on the observed
limb-brightened morphology of the outflow. Only \lesssim
20 per cent of the observed X-ray emission can come from
the volume-filling, metal-enriched, wind fluid itself.

We show that these observations are easily explained by, and
fully consistent with, the standard model of a superwind
driven by a starburst of NGC 253's observed power. This
observation implies that X-ray observations of starbursts do
not directly probe the energetic, metal-enriched, gas that
drives the observed superwind outflows. We discuss the
implications of these findings for the enrichment and
heating of the IGM by starburst-driven winds.

This work was supported by NASA through grants LTSA NAG56400
and GO0-1008X.

The author(s) of this abstract have provided an email address
for comments about the abstract:
dks@pha.jhu.edu